Method of producing ferrous castings having desired physical properties



June 27, 1944. REECE ET AL 2,352,408

METHOD OF PRODUCING FERROUS CASTINGS HAVING DESIRED PHYSICAL PROPERTIESv Filed July 3, 1941 5 Sheets-Sheet 1 HERBEPTA INVENTORS .EEEcE AND BYOLIVER 05MALLEK M v M June 27. 1944. H. A. REECE ET AL 2,352,408

METHOD OF PRODUCING FERROUS CASTINGS HAVING DESIRED PHYSICAL PROPERTIESFiled July 5, 1941 3 Sheets-Sheet 2 AUSTENITE AUSTENITE MARTENSITEGRAPHTE pEARuTE INVENTORS HERBERT A HERE AND OZIVEB SMAZZEY j A rronms.

June 27, 1944. REECE ET AL 2,352,408

METHOD OF PRODUCING FERROUS CASTINGS HAVING DESIRED PHYSICAL PROPERTIESFiled July 3, 1941 I 5 Sheets-Sheet 3 PEARLITE GRAPH \TE SORBO'PEARLITEFERR'TE PEARLITE 1' N VFN T0123 HERBERTA.REECE AND BY OLIVER SMALLEY'ATTORNEYS Patented June 27, 1944 METHOD OF PRODUCING FERROUS ST- INGSHAVING DESIRED PHYSICAL P OP- ERTIES Herbert A. Reece, ClevelandHeights, Ohio, and Oliver Smalley, Pittsburgln Pa., assignors toMeehanite Metal Corporation, a corporation of Tennessee Application July3, 1941, Serial No. 400,900

- Claims. (Cl. 148-3) Our invention relates to the art of making ferrouscastings.

In the production of foundry castings it is a desideratum to obtaincastings having a microstructure best suited to the type of service inwhich the castings are to be utilized. The metallographic structure ofcast iron is an important factor in the ability of the casting to meetthe particular requirements of the use to which the casting is to beput. There have been many approaches to the problem of obtaining thedesired metallographic structure in cast iron, some of which have beensuccessful to a limited degree but all of which have certain inherentdisadvantages, such as cost of the process, the inadequate control ofoperations, the lack of uniformity in results and inherent limitationsupon the scope of the processes.

For example, iron castings which are to be used for Diesel cylinders,brake-drums, crankshafts, liners, cams, gears and other machine partssubjected to rolling or sliding contact, require great wear-resistingproperties. To produce castings for such use requires a foundry practicewhich lends itself to the control of the microstructure of cast iron.One of the attempts to produce cast iron purporting to have physicalproperties suitable for wear resisting service is shown in United StatesPatent No. 2,200,765 issued to Bartholemew et a1. It is stated in thatpatent that the production of an iron casting having an austeniticstructure is of value for wear resisting uses as the casting may be "runin to effect a cold-working operation" of the material and a resultanthard and wearresstant surface.

However, the process suggested by the Bartholemew patent requires theexpensive and time-taking operations of allowing the castings to coolbelow the carbide critical range, of reheating them above roomtemperature, and of quenching the heated castings in a hot bath.Inasmuch as the castings are raised in temperature from that of roomtemperature, the heat treatment processes of Bartholemew and othersinvolves special heat treatment furnaces, incurs the risk of crackingthe casting, and is costly in operation. Moreover, due to severalfactors the structural stages through which the iron passes upon coolingcannot be completely and precisely retraced by merely heating the ironagain as suggested by Bartholemew. The present invention is based uponan entirely different principle from the process suggested by the saidBartholemew patent, obviates the disadvantages and difilculties of thatprocess and other heat treatment processes, and produces results notheretofore obtainable. Moreover, the present invention teaches thecontrol of the microstructure of cast iron in a manner and to an extentnot completed by said Bartholemew patent or other disclosures on heattreatment. The references herein to the Bartholemew patent or to theprior art in general are made only for the purpose of demonstrating thenovel nature and distinct character of the invention herein described.

It is an object of our invention to provide an economical and accuratemethod of'producing castings having desired improved and controlledphysical properties.

Another object is the provision of a method for controlling thestructure of iron castings.

Another object is the provision for retaining a. desired austeniticstructure in iron castings.

Another object is the provision for obtaining a sorbitic-austenitic or atroostitic-sorbitiic structure in an iron casting which would otherwisehave a predominantly pearlitic structure under the processes in standardpractice.

Another object is the provision for retaining varying amounts ofaustenitic or semi-austenitic structure in iron castings in accordancewith predetermined requirements.

Another object is the provision for obtaining an austo-troostitic or atroostitic-sorbitic or a sorbo-pearlitic structure in an iron castingwhich would otherwise have a pearlitic or a ferritic or aferro-pearlitic structure without this invention and under the processesutilized in standard practice.

Another object is the provision for obtaining asorbitic-troostitic or anall pearlitic structure in an iron casting which otherwise would exhibitprimary or secondary ferrite when produced under the processes instandard practice.

Another object is the provision for inhibiting the formation of freeferrite which may otherwise form under the processes utilized instandard practice.

Another object is the provision for eliminating free ferrite of poorwearing property from an iron casting. Y

Another object is the provision for inhibiting or arresting the normalstructural development of cast iron as would take place under theprocesses in standard practice.

Another object is the provision for obtaining cast iron having anultimate structure which would otherwise be a transitional structure of'the iron produced under the processes in standard practice.

Another object is the provision for fixing the structural condition ofcast iron at a desired stage of development. I

Another object is the provision for imparting wear resistance andtoughness to an iron casting.

A still further objectis the provision for obtaining cast iron whichpossesses superior wear resisting properties and which is at the sametime machinable.

Other objects and a fuller understanding of our invention will becomeapparent from the description herein taken in conjunction with theaccompanying drawings, in which:

Figure 1 is a diagram illustrating a typical time-temperature coolingcurve of a ferrous casting in a mold.

Figure 2 is a photomicrograph showing a sample of metal in a castingmade according to our invention.

Figure 3 is a photomicrograph showing another sample of metal in acasting made according to our invention.

Figure 4 is a photomicrograph showing a sample of metal in a castingleft in the mold until a modified transformation of the metal wascompleted.

Figure 5 is a photomicrograph showing a sample of metal of modifiedcomposition, as found in a casting shaken out at one temperature, and

Figure 6 is a photomicrograph showing a sample of metal 01' the samemodified composition, as found in a casting shaken out at a lowertemperature. The photomicrograph of Figures 2 to 6, inclusive, furnishedwith this application were made from magnifications of 1000 X, whichwere reduced in size one to two and a. half, to give a finalmagnification of 400 X.

The iron casting upon which the diagram of Figure l is based and whichis here given by way of example, was made of a cupola charge in thefollowing proportions:

Per cent Pig iron 10 Silvery 4.4 Spiegel l Bought and return scrap 49.6Steel 35 to which Nickel 1.5

Chromium .3

Molybdenum .6

has been added to the molten metal in the ladle The molten metal of thiscomposition was poured into Diesel engine cylinder liners of intricatedesign. The removal of the resultant casting from the mold, the timingof the removal and the cooling of the removed casting is the subjectmatter of this disclosure.

In the diagram of Figure 1 the ordinate represents the degreesFahrenheit temperature of the metal in the casting. The abscissarepresents the time in minutes during which the casting remains in themold. The line of the descending curve A to U represents the normalcooling curve in standard practice of the described iron casting withinthe mold, the full extension of the curve to the right being upon thebasis of the casting remaining in the mold until the casting is at ornear room temperature. This line AU may be referred to as the normalcooling curve as it shows in its extent the relative value in foundrypractice prior to our invention and under standard practice.

The following points and ranges marked along the descending curve denotestages in the microstructural development in the particular iron castingused as an example:

Point A indicates the temperature of the metal of the casting at thetime that the mold was filled with liquid metal, that is, thetemperature immediately after pouring. In the example of iron here givenpoint A is about 2550 F.

Point B indicates the temperature at the start of incipientsolidification. In the example here given point B is about 2280" F.

Point C indicates the main temperature where incipient solidificationends.

C to D indicates the temperature of main solidification and is thetemperature range in which takes place the main evolution of the latentheat of solidification. The temperature remains substantially at thesame temperature degree until point D is reached. In the example heregiven points C to D are about 2110 F., the temperature at D being justbelow 2110 F.

In compositions containing phosphorus point F would indicate thesolidification temperature of steadite, which consists of phosphide ofiron and a separated solution of FeaP in iron. This substance occurs byvolume about ten times that of the phosphorus content by weight and itssolidification temperature approximates 1740 to 1760 F. Steadite in grayiron is composed largely of a binary cellular eutectic of iron and ironphosphide. It may therefore be said that point F is the temperature ofsolidification of the phosphide eutectic in ferrous castings containingphosphorus. In the diagram of Figure 1, point F is indicated to belocated at about 1752 F.

Following the temperature range C--D, there is a series 01' changes inwhich the eutectic carbides break up into graphite and austenite. At thehigher temperatures preceding point D the metal containing less than4.3% carbon is a solid solution of cementite in high temperature orgamma iron and is called austenlte plus a liquid magma of carbondissolved in iron. Metal containing more than 4.3% carbon is a networkof cementite in a magma of carbon dissolved in iron. Depending on thecomposition of the metal the total structure will consist of one of thethree combinations (1) austenite and eutectic austermite-cementitealloy; (2) eutectic austenitecementite alloy 0r ledeburite; or (3)cementite alloy, respectively, according to whether the alloy had less,just the right amount, or more, carbon than the eutectoid proportion.

J, on the curve AU indicates the general location of the temperaturerange in which occurs the eutectoid crystallization of the solidsolution of cementite (FeaC) in iron (the said solid solution beingcalled austenite) to form the final eutectoid of cementite and ferritecalled pearlite. J may be referred to as 'the carbide critical range andis the temperature of the range where the carbide as pearlite or sorbiteis deposited from the solid solution of cementite in iron (austenite) toform the'final eutectoid of cementite and ferrite called pearlite.understood that the eutectoid temperature is not a precise or exacttemperature but is a range which may spread more or less than 100F. Thelocation and breadth of this range varies with the composition ofthemetal and addition of certain alloys such as nickel, silicon, manganeseor the like causes a shift in the location of this range.

According to the composition of the metal under consideration, the metalin the temperature ranges below and following the eutectoid point J maybe comprised of ferrite and pearlite, all pearlite, or cementite, orpearlite with free cementite. There may thus be found in the metal inthetemperature ranges following the eutectoid temperature J (incombinations and proportions dependent upon the composition of themetal), the constituents of cementite: cementite in conjunction withpearlite; or all sorbite or pearlite; or pearlite in conjunction withpatches of free ferrite. The proportion of carbon in the pearlitic formof metal is approximately .80% to .89%.

The carbon in cast iron also appears in free form as well as in thecombined form (such as combined in austenite, cementite, or pearlite).Under certain conditions and in varying ironcarbon proportions and underthe influence of diflerent graphitizing agents, some carbon will becomedissociated from the iron and is precipitated out as graphite.

The principal transition in the microstructure of the 'metal during thedownward cooling curve following the temperature CD is the progressivechange of austenite to cementite or carbide and pearlite, or topearlite, or to pearlite and ferrite. There are many other modified andtransitional stages in the microstructure of the metal during thedownward temperature curve dependent upon the character of the charge ofmaterials melted and the chemical composition of the metal underconsideration. There are many well known names (such as austenite,martensite,

troostite, sorbite, and pearlite or combinations of these) which havebeen given to these modified forms of structure .between austenite andpearlite and to mixtures containing them.

Inasmuch as the physical properties of the ulti mately produced ironcasting and its ability to meet particular service requirements dependupon the internal microstructure of the cast iron, the selection andcontrol of the ultimate structural form is most important. in foundrypractice. In the processes of standard practicev and without ourinvention, the casting is left in the mold until the casting is cooledappreciably below the critical range of temperature denoted as being inthe general location of J and until the casting has cooled tosubstantially room temperature. Below this critical temperature rangethe metal has substantially completed the transitional structuraldevelopment preceding and within'the eutectoid temperature range andbecomes converted to the ultimate forms of pearlite, or pearlite andfree ferrite, or pearlite and free carbide, depending upon the natureand composition of the cast iron and upon the design and form of thecasting under consideration. The conversion to the said ultimate-form offree ferrite is particularly dependent upon the time that the cast- Itis to be ing remains in, and is subject to the influence of, the mold.

When castings are poured the temperature of the mold or the molding sandand c'oresandim- 'mediately adjacent the casting may remain above thetemperature of iron, particularly the sand of the core, and may retainthe heat longer than the iron alone would. This retained heat may causea breakdown of the metal structure through the austenitic andsorbo-pearlitic stages to the point where free ferrite is formed. Thepresence of such free ferrite provides poor wearing properties andreduces the physical strength characteristic of the casting. It isdesirable that the breakdown into ferrite in the casting or in anyportion of the casting be prevented and this may be done by an arrestingor inhibiting of the normal and abnormal structural changes otherwiseoccurring.

Some of the transitional forms of iron and particularly austenite,troostite and sorbite, and

as to what occurs in the running in or cold working" operation it isknown that the retention of some of the transitional forms of the ironsuch as austenite, troostite and sorbite is highly desirable for wearresisting service.

In order to meet the problem of machining the casting, the castingsshould not be made' too hard and tough. To obtain castings of requiredhardness and toughness and yet machinable a balance is reached byselecting and obtaining the transitional stage of structural form bestmeeting all requirements, as for example, cast iron containing in properproportions austenite and troostite, or troostite-sorbite or sorbite andfine lamellar pearlite or fine lamellar pearlite free from any patchesof ferrite.

In the practice of our invention the iron casting is shaken out orremoved from the mold at any early stage and before the normalstructural development of the metal has been completed. The time atwhich the casting is shaken out after pouring depends upon thepredetermined microstructure desired for a particular use, that is, thetime depends upon the transitional stage or structural development whichit is desired to secure in the ultimate casting. In all cases thecasting is shaken out of the mold while still hot and the shaking out isat least commenced, and preferably completed, before the casting haspassed or cooled appreciably below the eutectoid temperature J.

In some cases it is most suitable for an intended purpose to shake thecasting out of the mold while at a high temperature on the normalcooling curve and as close to point D as possible. In other cases, it ismost suitable for an intended purpose to shake the casting out of themold at or in the neighborhood of an intermediate temperature G. Forother results, it is preferable to shake the casting out of the moldwithin the critical range but before the eutectoid solidification hasbeen completed. In other cases, it is most suitable for an intendedpurpose to shake the casting out oi the mold at a temperature just aboveand preceding the carbide critical temperature J. In other instancesother temperatures and time periods along the cooling curve, such as forexample, at point D, at point E, or at point H, may be best suited forthe separation of the casting from the mold to obtain the predeterminedmicrostructure desired in the metal.

The operation of shaking the casting from the mold is not instantaneousand a lapse of some time takes place between the beginning and thecompletion of the shaking out operation, depending on the size andcharacter of the casting. The time required for the removal of thecasting from the mold is represented by a short length or section of thenormal cooling curve between the commencement and the completion of theshaking out operation.

After removal of the casting it is cooled by exposure to the air at amuch more rapid rate than it would have normally cooled in the mold.

In other words, a new cooling curve is established for the casting afterremoval and this new cooling curve is entirely independent of theinsulating and heat retaining influence of the mold. The new coolingrate being relatively rapid tends to secure the structure of the metalin the transitional stage at which the casting was removed from the moldand to arrest further structural development in the metal.

The rate of the new cooling curve after separation of the casting fromthe mold may be adjusted or regulated. In some cases we expose theremoved casting to atmospheric air to cool it and the new cooling curveis thus set at one rate. After removal of the casting from the mold thenew and independent cooling curve for the casting may be regulated in anumber of ways. To retard the new cooling rate (but of course notretarded to the slow rate of the normal cooling curve of the casting inthe mold), the casting may be sheltered by suitable means. To acceleratethe new cooling rate, an air blast may be blown upon the casting. Whenstill a more rapid cooling rate is desired we subject the casting to arefrigerated atmosphere or to a spray of water or other cooling liquid.By such means a line regulation of the new cooling curve may beobtained, the new cooling curve being entirely distinct and independentof the normal cooling curve of a casting remaining in the mold as instandard practice. The more rapid the rate of the new cooling curve,that is, the more it departs from the normal cooling curve of standardpractice, the more of the early transitional forms of the metal areretained and the later transitional forms inhibited. To obtain just thedesired mixture or proportion of early forms and later forms, the rateof the new cooling curve is adjusted.

The arresting or inhibiting of the formation of either primary orsecondary free ferrite may be brought about by this new cooling curveadjusted to requirements after the separation of casting and mold. Bythe use of this controlled cooling the entire casting or portion thereofas would otherwise be converted into ferrite may be retained in anydesired structural form, as for example, austenite, martensite, sorbiteor line lamellar pearlite. Such structural forms provide r y running inquality so as to assure superior wear resistance and provides for "coldworking somewhat similar to that found in heat-treated carbon steels,alloy steels and iron. Castings thus produced have superior and improvedwear resistance properties over those produced by the processes instandard practice.

In the practice of our invention castings are shaken out of the mold andexposed to atmospheric air in one form or another, such as still air oran air blast. This operation is performed in the light of the discoveryand vteachings here set forth to predeterminately obtain the desiredresults in the service of the casting.

Examples of the practice of our invention are illustrated in Figure 1 inwhich is demonstrated sample cases of removal of the castings and thesubsequent cooling in air. In the first sample case, point K indicatesthe time and the temperature oi. the example casting when stripping orshaking out was commenced and point L indicates the time and temperaturewhen the separation of the casting and mold was completed. The line K-L,M indicates the new cooling curve or cooling range of the casting afterseparation from the mold. The photomicrograph of Figure 2 illustratesthe ultimate structural form of the metal in our sample casting afterbeing shaken out and cooled according to the line K-L, M, that is, whenshaken out about 20 minutes after pouring of the casting and then cooledin still air. The resultant structure is shown as being composed ofaustenite, martensite, sorbite and graphite.

Upon the swinging of the new cooling curve from point M along the brokenline to point V by the use of an air blast on the casting or othersuitable means, then more austenite is retained. Upon the swinging ofthe new cooling curve from point M along the broken line to point Z bythe use of sheltered cooling then less austenite is retained.

In a second sample case, point N indicates another time and temperaturewhen the breaking of the mold was commenced and 0 indicates the pointwhere stripping was completed. The line N-O, P indicates the new coolingcurve of the casting exposed to the air. The photomicrograph of Figure 3illustrates the ultimate structural form of the metal in our samplecasting after being shaken out and cooled according to the line N0, P,that is, when shaken out about one hour after pouring of the casting andthen cooled in still air. The resultant structure ,is shown ascontaining austenite, martensite,

sorbite, sorbo-pearlite, pearlite and graphite in proportions differingfrom the 20 minute shakeout of line K-L, M, and particularly in that a.lesser amount of austenite and martensite is present. The new coolingcurve N-O, P may be varied by swinging point P to point X and theresulting structure is modified to some extent.

We also show the result of shaking the casting out of the mold at thecommencement of the eutectoid temperature J, he stripping of the moldbeing completed soon after the eutectoid temperature. In this instanc.-,R, in Figure 1. represents the approximate temperature when the breakingof the mold was commenced and 8 represents the approximate temperaturewhen stripping was completed. The line R-S, T represents the new coolingcurve of the removed casting. The photomicrograph of Figure 4 shows theearlitic structure resulting from leaving the example casting in themold 2 hours and live I minutes before stripping. The casting in thisinstance has a microstructure resulting from leaving in the mold untilthe decomposition or transformation of the austenite has been completed.The microstructure shown does not exhibit free patches of ferrite whichmight otherwithdrawing the castings from the molds at selecterltemperatures and within certain time limits prior to the passing. of thecritical stages and by cooling the casting or a portion of the cast--ing out of the mold at proper cooling rates to retain the desired typeof structure. By this control the resulting hardness of the casting maybe increased as required, the retention of austenite, martensite,troostite, sorbite and pearlite, and the desired proportions thereof,greatly eifecting the physical properties of the casting and its use inservice. The method here disclosed eliminates the use of subsequent heattreatment, gives better control of results, and provides a means ofobtaining results not heretofore obtainable.

Variations and modifications are of course suggested by the presentdisclosure. For example. the casting might be shaken out at point E toproduce one structural composition, shaken out at point G to produceanother structural composition, or shaken out at point B to producestill another structural composition. The design, size and weight of thecasting are variable factors which are to be taken into consideration intiming the shaking out operation to obtain the desired microstructure inthe ultimate metal obtained. Likewise, the character of the molten metalmay be varied to fill requirements. For example, the following chargemay be used for the casting here discussed:

The metal of this modified composition was poured into molds in theusual manner and after an interval of time decided on by the type ofcasting, the section of casting poured and the composition of the metal,the castings were shaken out of the mold. Figure is a photomicrograph ofa casting containing metal of this modified composition when shaken outat a temperature above the critical range and cooled at an independentand controlled rate. By way of comparison, Figure 6, being aphotomicrograph of a casting of this same modified composition afterbeing left in the mold until after the critical range had beencompletely passed and decomposition of some of the metal into freeferrite had taken place. The patches of free ferrite resulting fromleaving the casting in the mold until the break-down into ferrite hadcommenced is apparent in the photomicrograph of Figure 6. v

Another sample composition which may well be used in making castings forcarrying out our invention, is made of a charge of:

Per cent Pig iron 25 Cast iron scrap 50 Steel 25 and having a chemicalanalysis of:

. Per cent Silicon 1.6 Manganese .9 Phosphorus v .2 Total carbon 3.25

Although alloys were shown as added to the that the charge need notinclude the alloys. The eiiect of different alloys in shifting thecritical range of the metal in the casting is well known. Our inventionis practiced with good results regardless of the efiect of these alloysupon the critical range although the shifts in the critical range aretaken into account in determining the timing of the shake-out of thecasting at required temperature.

However, the governing principles of our invention remain the same inthe modifications of the specific values of time and temperature givenin our present disclosure, such as in variations in the chemical contentof the metal or in changes of other factors.

The disclosure herein includes the processes described in the appendedclaims and suggested in the accompanying drawings, which processes areincorporated in, and made a part of, this patent specification. I

Although we have described our invention with a certain degree ofparticularity, it-is understood that the present disclosure has beenmade only by way of example and that numerous changes in the details ofthe process, modifications in the steps undertaken, variations in thematerials" used, and diiferent values of time and temperature, may beresorted to without departing from the spirit and the scope of theinvention as hereinafter claimed.

We claim as our invention:

1. The improved method of producing iron castings formed in the ultimateshape of use in service and possessed of desired physical wear resistingproperties resulting from securement of austenite in the iron at roomtemperature, comprising the steps of pouring into a foundry mold havinga cavity of said ultimate shape molten iron having a totalcarbon-silicon content of from about 4.06% to about 4.85%, of whichpercentages about 1.10% to about 1.60% comprises silicon, to inherentlyproduce thereby iron having a volume shrinkage characteristic on coolingof 2% or more and having a microstructure progressively changing fromaustenite to pearlite during normal cooling of the casting in the mold;separating the mold and the formed casting after solidification butbefore the casting has cooled in the mold to below the eutectoidcritical range; and immediately cooling the separated casting inatmosphere through the eutectoid critical range to approximate room.temperature at a controlled rate greatly accelerated from the normalcooling rate of such a casting remaining in the mold to thereby arrestthe normal change of'austenite to pearlite for securing austenite in thesaid ultimate casting at room temperature.

2. The improved method of obtaining the tough wear resisting quality ofaustenite in an iron casting at temperatures of service for the casting,comprising the steps of: providing molten iron having a totalcarbon-silicon content of from about 4.06% to about 4.85%, aboutonefourth to one-third of said carbon-silicon content being comprised ofsilicon; pouring said molten iron into a foundry mold having a cavityapproximating the shape of the casting for use in service; shaking thecasting out of the mold after main solidification of the said iron butwhile still at an elevated temperature produced solely by the latentheat of the iron and prior to the cooling of the casting in the moldthrough the carbide critical range; immediately cooling the casting inatmosphere to accelerate the cooling of the casting through the carbidecritical range to inhibit the decomposition of austenite as oc-' curringin such a casting slowly cooled in the mold through the carbide criticalrange; and controlling the rate of said accelerated cooling to obtainthe desired degree of retention of austenite in the casting attemperatures below the carbide critical range in which the casting isused in service.

3. The improved method of producing iron castings formed in the ultimateshape of use in service and possessed of desired physical propertiesresulting from securement of austenite in the iron at room temperature,comprising the steps of: Pouringinto a foundry mold having a cavity ofsaid ultimate shape molten iron having chemical proportions insubstantially the neighborhood of the following values: 1.46% silicon,.85% manganese, 3.14% total carbon, 1.27% nickel, .42% chromium, 155%molybdenum, to inherently produce thereby iron having a volume shrinkagecharacteristic on cooling in the neighborhood of 2% or more and having amicrostructure progressively changing from austenite to pearlite duringnormal cooling of the casting in the mold; separating the mold and theformed casting after solidification but before the casting has cooled inthe mold to below the eutectoid critical range; and immediately coolingthe sepa-- rated casting in atmosphere through the eutectoid criticalrange to approximate room temperature at a controlled rate greatlyaccelerated from the normal cooling rate of such a casting remaining inthe mold to thereby arrest the normal change of austenite to pearlitefor securing austenite in the said ultimate casting at room temperature.

4. The improved method of producing iron castings formed in the ultimateshape of use in service and possessed of desired physical propertiesresulting from securement of austenite in the iron at room temperature,comprising the steps of: pouring into a foundry mold having a cavity ofsaid ultimate shape molten iron having chemical proportions insubstantially the neighborhood of the following values; 1.10% silicon,1.05% manganese, 2.96% total carbon, .12% phosphorus, .078% sulphur, toinherently produce therebyiron having a yolume shrinkage characteristicon cooling in the neighborhood oi 2% or more and having a microstructureprogressively changing from austenite to pearlite during normal coolingof the casting in the mold; separating the mold and the formed castingafter solidification but before the casting has cooled in the mold tobelow the eutectoid critical range; and immediately cooling theseparated casting in atmosphere through the eutectoid critical range toapproximate room temperature at a controlled rate greatly acceleratedfrom the normal cooling rate of such a casting remaining in the mold tothereby arrest the normal change of austenite to pearlite for securingaustenite in the said ultimate casting at room temperature.

5. The improved method of producing iron castings formed in the ultimateshape of use in service and possessed of desired physical propertiesresulting from securement of austenite in the iron at room temperature,comprising the steps of: pouring into a foundry mold having a cavity ofsaid ultimate shape molten iron having chemical proportions insubstantially the neighborhood oi the following values; 1.6% silicon,

.9% manganese, 3.25% total carbon, and 3% phosphorus, to inherentlyproduce thereby iron having a volume shrinkage characteristic on coolingin the neighborhood of 2% or more and having a microstructureprogressively changing from austenite to pearlite during normal coolingof the casting in the mold; separating the mold and the formed castingafter solidification but before the casting has cooled in the mold tobelow the eutectoid critical range; and immediately cooling theseparated casting in atmosphere through the eutectoid critical range toapproximate room temperature at a controlled rate greatly acceleratedfrom the normal cooling rate of such a casting remaining in the mold tothereby arrest the normal change of austenite to pearlite for securingaustenite in the said ultimate casting at room temperature.

HERBERT A. REECE. OLIVER SMALLEY.

